The present invention relates to a control device for the glue nozzles of a machine for gluing together at least two paper webs provided with recurring form designs to produce multi-part sets of continuous forms. A control device of this kind can also be used to control other devices for joining together two or more paper webs to produce multi-part sets if, by way of exception, a joining technique other than gluing should be chosen. One possible other joining technique consists, for example, of pulling an adhesive tape through the sprocket holes at the edges of the continuous paper webs.
Continuous form sets frequently consist of several layers, e.g., for multi-part invoice form sets. Each layer consists of a paper web with recurring form designs. The webs must be precisely aligned in relation to each other, so that associated form designs are superposed so as to permit copies to be made. The precisely aligned paper webs are joined together, usually glued together, and then provided with a cross perforation by a cross-perforation cylinder.
In the majority of multi-part sets of continuous forms it is not permitted to make continuous glue joints in the form of longitudinal strips. As a rule, it is required that the glue strips be interrupted, and it may also be necessary to provide glue strips in different locations and of different length between different paper webs. The glue nozzles applying the glue must thus be switched on and off precisely as a function of the position of a form with respect to the glue nozzle. This necessitates a control device.
A known control device for this purpose is, for example, a position-encoder disk connected to the shaft of the cross-perforation cylinder. The position-encoder disk is provided with segment-shaped aluminum strips. During rotation of the disk, these aluminum strips are sensed by inductive sensors. Each inductive sensor is connected to a control circuit via which the output stage for an associated glue nozzle is controlled. The lengths and locations of the aluminum strips are chosen so that the glue nozzle controlled by the inductive sensor applies the glue to the form precisely in the right area. The length and location of each aluminum strip must be determined empirically.
If used for changing form designs, such a known control device requires a large amount of labor. It is necessary to operate one position-encoder disk for each nozzle and to use different position-encoder disks for different designs. As a result, a large number of position-encoder disks have to be kept in stock, and much changeover work is required. When changing from a size of, e.g., 8 inches to one of, e.g., 12 inches, the position-encoder disks must be turned relative to the cross-perforation cylinder even if the relative dimensions of the gluing pattern remain constant. This is due to the fact that the glue nozzles are permanently attached to a gluing machine, while the beginnings of the forms shift in relation to the glue nozzles if form lengths are changed. This shift must be compensated for by turning the position-encoder disks about the shaft of the cross-perforation cylinder.